The two major amino-oligopeptidases that play an important role in the assimilation of dietary protein will be studied by use of radioimmunoassay to identify enzymatically inactive precursors within the depths of the intestinal cell. It is known that the mature enzymes are constituents of the intestinal brush border membrane and radioactive probes including 125I and tritiated borohydride will be used as potential covalent probes to establish the portions of the enzymes that are available at the intestinal surface, within the lipoidal membrane, and at the interior surface of the limiting intestinal membrane. Finally, studies of the in vivo synthesis and degradation of the amino-oligopeptidases will be carried out by pulse labeling with radioactive amino acid precursor and isolation of amino protein by quantitative immunoprecipitation. In this way, it should be possible to determine whether the rate of turnover of the intestinal cells or the rate of degradation of the protein within the individual cell is rate limiting in the modulation of enzyme activity. Finally, different animals will be fed regular diet, low protein diet, high protein diet or deprived of pancreatic proteases by use of pancreatectomy in order to determine the effect of constituents of the diet and the pancreatic endopeptidases on the regulation of these enzymes. BIBLIOGRAPHIC REFERENCE: Wojnarowska, F. and Gray, G.M. Intestinal surface peptide hydrolases: identification and characterization of three enzymes from rat brush border. Biochim Biophys Acta 403:147, 1975.